1. Field of the Invention
The present invention is directed to a vane pump. More particularly, the present invention is directed to a vane pump which is especially adapted for pumping cryogenic liquids.
2. Brief Description of Prior Art
Vane pumps adapted for pumping fluids, particularly liquids, have been known for a long time. As is known in the art, vane pumps comprise a particular type or class of positive displacement pumps and have a non-rotating stator housing which forms a chamber, and a rotor which is eccentrically placed in the housing to rotate therein. A plurality of vanes are mounted for in-and-out sliding movement, substantially in the radial direction. The vanes stay in contact with the interior wall of the chamber and force the fluid (usually liquid) to flow from an inlet port towards an outlet port. Problems which various constructions of vane pumps strive to solve relate to movement of the vanes within the slots formed in the rotor, friction generated between the vanes and the stator housing, and the quality of the seal formed between the vanes and the stator housing. Generally speaking, as it will be well appreciated by those skilled in the art, friction between the vanes and the stator is undesirable, an effective seal between the vanes and the stator housing is desirable, and ideally the vanes should move in-and-out of their respective slots in the rotor with minimum hindrance and friction. U.S. Pat. Nos. 3,988,083, 3,955,540, 4,451,219, 4,184,821, 4,299,546, 4,410,305, 4,209,286, 4,225,295, 4,212,603, 870,290, 118,993, 1,952,142, 4,088,426, 4,253,809, 2,672,282, British Patent Specification No. 259,346, and German Patent Nos. 455,476, 458,384, exemplify various approaches of the prior art to rotary vane pumps, rotary vane compressors and related devices (such as rotary engines), which attempt to accomplish the above-noted goals.
Rotary vane pumps used for pumping cryogenic liquids must, generally speaking, meet more exacting requirements than vane pumps used in other applications. As is known, cryogenic liquids, such as liquefied hydrogen, liquefied nitrogen and liquefied helium are extremely cold, lack substantial lubricating qualities, and have low viscosity. Extreme cold temperature usually generates a problem in the operation of any mechanical device. This problem is exacerbated in vane pumps for cryogenic liquids where the lack of lubricity of the pumped cold liquid causes additional problems of friction, and where input of heat generated by friction is particularly undesirable. Moreover, the low viscosity of the pumped cryogenic liquids permits significant leakage through relatively small openings, and therefore, for efficient operation particularly effective seals would be required. The present invention provides a vane pump especially suited for pumping cryogenic liquids which is designed to address and overcome or alleviate the above-noted problems.